1. Field of the Invention
This invention relates to methods for fabricating microfibrous electrochemical cells, specifically fuel cells, by using a removable substrate material as a support for additional coatings thereon, while such removable substrate material is subsequently removed to create a lumen in the microfibrous fuel cells to allow passage of fluid.
2. Description of the Related Art
The microcell technology is described in U.S. Pat. Nos. 5,916,514; 5,928,808; 5,989,300; 6,004,691; 6,338,913; 6,399,232; 6,403,248; 6,403,517; 6,444,339; and 6,495,281, all to Ray R. Eshraghi. The microfibrous cell structure described in these patents comprises hollow fiber structures with which electrochemical cell components are associated.
The aforementioned Eshraghi patents specifically describe a microfibrous fuel cell, which has an inner current collector, a hollow fibrous membrane separator containing an electrolyte medium, an outer current collector, and an inner and outer electrocatalyst layer on the inner and outer surface of the membrane separator.
Such microfibrous fuel cell further comprises an elongated lumen within the hollow fibrous membrane separator, which provides a fluid path to allow the passage of either fuel (such as hydrogen or methanol) or oxidant (such as oxygen). The presence and clearance of such fluid path is essential for the microfibrous fuel cell to properly perform its energy-generating function properly.
Conventional methods for fabricating such microfibrous fuel cell with the required fluid path involves formation of a hollow fibrous membrane separator by extruding a membrane-forming polymer through an orifice of an extrusion mold referred to as “spinnerette,” either before insertion of the inner current collector, or concurrently around the inner current collector. A liquid or gas is blown through a bore-forming tube located in the center of the extrusion orifice, so as to form a lumen within the fibrous membrane separator so formed. The inner diameter of the hollow fibrous membrane separator is slightly larger than the outer diameter of the inner current collector, therefore leaving a fluid path for passage of fluid fuel therethrough. For more details of such conventional methods, see the U.S. Pat. Nos. 5,916,514; 5,928,808; 5,989,300; and 6,004,691.
However, such conventionally methods depend on use of a liquid or a gas as a lumen-forming agent, which is a fluid and cannot provide sufficient support against deformation caused by external force during the manufacturing process. Therefore, the hollow fibrous membrane separators formed by such methods may suffer from flat spots, which refers to blockage of the lumen or the fluid path within specific sections of the membrane separators, due to deleterious external force applied to the membrane separators before the membrane separator wall becomes fully solidified.
There therefore is a continuing need in the art to provide easier and faster ways to produce microfibrous fuel cells, with little or no blockage of the required fluid path therewithin.
Moreover, the conventional methods for fabricating the microfibrous fuel cell form the inner electrocatalyst layer either simultaneously with the hollow fibrous membrane separator via co-extrusion, or after the hollow fibrous membrane separator has already been formed. The co-extrusion process is very complicated, and the inner electrocatalyst and the hollow fibrous membrane layers formed by such process are also subject to significant deformation, due to the fact that such co-extrusion process provides little or not support to the newly-formed inner electrocatalyst and hollow fibrous membrane layers before complete solidification thereof. Subsequent catalyzation of the hollow fibrous membrane separator is not only complicated, but also increases the risk of blocking the required fluid path within such hollow fibrous membrane separator during the catalyzation steps.
It is therefore an object of the present invention to provide a substrate-supported process for producing the microfibrous fuel cells, in which an inner electrocatalyst layer can be first formed on a removable substrate, and a membrane-forming material layer is formed on and supported by such inner electrocatalyst layer, wherein the removable substrate can be subsequently removed to form the required fluid path within the membrane-forming material layer. Such substrate-supported process provides structural support for both the inner electrocatalyst layer and the membrane-forming material layer before complete solidification thereof. It not only simplifies the overall manufacturing process, but also significantly improves the quality of the microfibrous fuel cells formed thereby.
Other objects and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims.